Axle driving apparatus

ABSTRACT

A housing cannot be made compact by only securing a space corresponding to a reservoir tank at the upper part of the housing, and the space at the upper part of the housing cannot be utilized if the reservoir tank is integrally provided to the upper part of the housing. An axle driving apparatus comprising a tubular reservoir tank erected on the upper surface of the upper wall surface of the housing for accommodating an HST, wherein, since the reservoir tank is thinly elongated and is freely bendable, it can be disposed in a limited space. The housing is divided into a first room and a second room with which the reservoir tank communicates. Further, a first magnet is disposed at a position where the first and second rooms are connected, and a second magnet is disposed in the proximity of an oil filter connected to a closed circuit of the HST so that impurities can be removed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a reservoir tank attached to anaxle driving system in which a hydrostatic transmission (hereafterreferred to as HST), an axle, and a drive train for connecting the HSTand the axle for driving are housed in a common housing.

[0003] 2. Related Art

[0004] Conventionally, a housing that houses an HST is filled withhydraulic oil that is also used as lubricating oil. A temperature of thehydraulic oil is increased by driving the HST. The increase intemperature of the hydraulic oil results in an increase in its volume.In order to receive the increase in the volume, a technique of providinga reservoir tank on an outside of the housing or forming space having avolume corresponding to the increase within the housing to form areservoir room is known.

[0005] For example, there is a technique disclosed in U.S. Pat. No.4,987,796 or U.S. Pat. No. 5,440,951.

[0006] However, an axle driving apparatus that utilizes a reservoir tankstructure. requires additional space, a mounting member for mounting thereservoir tank, and piping for connecting the reservoir tank and thehousing. In addition, the number of man-hours required for assemblyincreases, the reservoir tank is difficult to handle, and costincreases.

[0007] By positioning the reservoir tank at an upper portion of thehousing, a vertical length of the housing increases to inhibitminiaturization of the axle driving system and an air layer is createdin the housing to cause air to be swallowed in oil when the oil withinthe housing is stirred. If this oil is charged into a closed circuit ofthe HST as the hydraulic oil, volume efficiency of the HST is reduced,which may generate noise or reduce durability.

[0008] Further, it is difficult to integrally form the reservoir tank atthe upper portion of the housing for a lawn tractor having a reardischarge method, because a chute passes above the axle driving system.

SUMMARY OF THE INVENTION

[0009] According to the present invention, a tubular reservoir tank ismounted to stand on an upper face of an upper wall-face of a housingthat houses an HST including a hydraulic pump and a hydraulic motor. Thereservoir tank communicates with an oil reservoir within the housing.Therefore, it is possible to easily mount the reservoir tank by a simplestructure, to form the reservoir tank from low-priced members, and toreduce cost.

[0010] The reservoir tank is formed of a tubular member. Therefore, ifthere is a member such as a chute that is related to the vehicle mainmachine above the housing, it is possible to mount the reservoir tank bybending the reservoir tank. Therefore, it is possible to easily mountthe reservoir tank by causing the reservoir tank to make way for themember that interferes with the reservoir tank, thereby increasing thenumber of applications in which the axle driving system may be used.

[0011] The housing is partitioned into a first room, housing the HST anda second room, housing an axle and a gear train for transmitting powerfrom the hydraulic motor to the axle. The first and second roomscommunicate with each other such that the oil with which both the roomsare filled can circulate between both the rooms. The reservoir tank isdisposed on the second room. Therefore, it is possible to position amounting portion of the reservoir tank in a high position, therebyeasily purging air generated within the reservoir tank. Because thereservoir tank may be disposed in a position isolated from the pumpshaft, it is possible to easily prevent the reservoir tank frominterfering with a rotary member such as an input pulley or a coolingfan.

[0012] A communicating position connecting the first room and the secondroom allows oil to pass there between. A filter member for removingimpurities included in oil is disposed in the communicating position.Therefore, it is possible to remove impurities included in the oil whenthe oil circulates between the first room and the second room due to thevariation in volume of the respective rooms which occurs with a changein oil temperature or stirring by actuation action of the HST orrotation of a gear. The impurities can be removed by means of the filtermember disposed in an oil hole for hydraulic oil of the HST, the oilwithin the first room can be cleaned, and durability of the HST can befurther improved.

[0013] Because the filter member is formed of a magnet, the filtermember can be formed at low cost and can be miniaturized. Therefore,limitations to a place where the filter member is disposed can bereduced, durability of the filter member is high, and the filter membercan be cleaned easily.

[0014] A closed circuit is formed by providing an oil path to a centersection to which a hydraulic pump and a hydraulic motor in the HST aremounted, an oil hole opening at the center section for supplyinghydraulic oil to the closed circuit is connected to an oil filterdisposed in an oil reservoir, and a magnet is disposed in the oilreservoir in a vicinity of the oil filter. Therefore, it is possible tocause the magnet to collect iron powder before it is drawn into the oilhole and to easily remove the harmful iron powder before it enters theclosed circuit of the HST.

[0015] The magnet is disposed such that the magnet acts on the hydraulicoil after passing through the oil filter and before entering the oilhole. Therefore, if there is extremely fine iron powder that has passedthrough the oil filter, the iron powder can be collected by the magnetand prevented from entering the closed circuit of the HST, therebyincreasing life of the HST. Because only small iron powder is collectedby the magnet, an amount of iron powder collected by the magnet is smalleven after use of the magnet for a long term and frequency ofmaintenance can be reduced.

BRIEF DESCRIPTION OF THE FIGURES

[0016]FIG. 1 is a general side view of a lawn tractor to which an axledriving system of the present invention is mounted.

[0017]FIG. 2 is a sectional view taken in a direction of an arrow A-A inFIG. 1.

[0018]FIG. 3 is a back perspective view of an axle driving system.

[0019]FIG. 4 is a sectional view taken in a direction of an arrow B-B inFIG. 2.

[0020]FIG. 5 is a sectional view taken in a direction of an arrow C-C inFIG. 4.

[0021]FIG. 6 is a sectional view taken in a direction of an arrow D-D inFIG. 4.

[0022]FIG. 7 is a sectional view taken in a direction of an arrow E-E inFIG. 4.

[0023]FIG. 8 is a sectional view taken in a direction of an arrow F-F inFIG. 4.

[0024]FIG. 9 is a sectional view showing another embodiment in which amagnet is disposed in the vicinity of an oil filter.

[0025]FIG. 10 is a perspective view of a mounting seat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In FIGS. 1, 2, and 3, a lawn tractor of a rear discharge methodhas a vertical crankshaft-type engine 100 disposed on a front portion ofa bodywork frame 101. Steerable left and right (front) follower wheels102, 102 are suspended from the front portion of the bodywork frame 101,an axle driving system 6 having left and right (rear) driving wheels103, 103 is suspended from a rear portion, a grass box 104 is mounted toa rear end by a working machine mounting device (not shown) such thatthe grass box 104 can be hoisted and lowered, and a mower 105 is mountedto a lower portion of the bodywork between the follower wheels 102, 102and the driving wheels 103,103 through a hoisting and lowering mechanism(not shown). A discharge opening of the mower 105 and an entrance of thegrass box 104 are connected through a chute 106. The chute 106 extendsdiagonally upward and rearward from an upper portion of the mower 105,passes above the axle driving system and between the left and rightdriving wheels 103, 103, and connects to the entrance of the grass box104. Therefore, grass mowed by the mower 105 is blown rearward, passesthrough the chute 106 and between the left and right driving wheels 103,103, and is housed in the grass box 104.

[0027] As shown in FIG. 1, two pulleys 108 and 109 are fixed onto avertical output shaft 107 of the engine 100. The pulley 108 has anelectromagnetic clutch and transmits power through a belt 110 to aninput pulley 112 fixed onto an input shaft 111 of the mower 105 to drivethe mower 105, thereby rotating a cutting blade 115 of the mower 105. Asshown in FIG. 3, five tension pulleys 114, pivoted on the bodywork frame101, allow a belt 113 to navigate around the chute 106. The belt 113 isattached to the other pulley 109 and an input pulley 43, which is fixedonto a pump shaft 3. Pump shaft 3 is an input shaft projecting upwardfrom the housing of the axle driving system 6. A reference numeral 44designates a cooling fan for cooling the axle driving system and fixedto a lower face of the input pulley 43 on the pump shaft 3.

[0028] As shown in FIG. 3, the axle driving system 6 is hung on left andright mount members 101 a, 101 a which are parts of the bodywork frame101. Left and right axles 7L and 7R project from side faces of thehousing of the axle driving system 6 and the driving wheels 103, 103 aremounted to end portions of the axles 7L and 7R.

[0029] Next, in FIGS. 4 to 8, a general structure of the axle drivingsystem 6 will be described. The housing of the axle driving system 6 isformed of two housing members, i.e., an upper housing 1 and a lowerhousing 2, which are joined to each other at their flat and peripheraljoint faces in a horizontal plane. At the joint face of the housing,bearing portions of a motor shaft 4 and a counter shaft 26 are provided.The axles 7L and 7R are disposed in parallel with the joint face of thehousing. The bearing portions of the axles 7L and 7R are displacedupward from the joint face and disposed within the upper housing 1 torotatably support the axles 7L and 7R. The respective axles 7L and 7Rare connected in a differential manner by a differential gear 23 andopposite ends of the axles 7L and 7R project outward from left and rightouter walls of the housing.

[0030] An inside of the housing is partitioned by an inner wall 8 into afirst room R1 for housing the HST and a second room R2 for housing adrive train. The drive train is formed of a plurality of gears fortransmitting power from the motor shaft 4 to the differential gear 23and the axles 7L and 7R. The inner wall 8 is formed of a portionextending along and in parallel with a longitudinal direction of theaxles 7L and 7R and a portion extending in a direction perpendicular tothe longitudinal direction. These portions are formed seamlessly and thefirst room R1 is adjacent to the second room R2. The inner wall 8 isformed of a wall portion hanging from an inside of the upper housing 1toward the joint face and a wall portion standing from an inner wall ofthe lower housing 2 toward the joint face. End faces of the upper andlower wall portions are placed on each other at the joint face, therebypartitioning the inside of the housing into two independent rooms.

[0031] The first room R1 is disposed at the rear of the axles 7L and 7Rand on the left of a power transmission device for transmitting powerfrom the motor shaft 4 to the differential gear 23 in the housing asshown in FIG. 4. In the first room R1, a center section 5 constitutingthe HST is detachably mounted to the inside of the upper housing 1. Thecenter section 5 is disposed such that a longitudinal direction of thecenter section 5 is in a longitudinal direction of the bodywork and issubstantially perpendicular to the axles 7L and 7R. A vertical face isformed at a rear portion of the center section 5, a motor attachmentface 41 is formed on the vertical face, and a hydraulic motor 51 isdisposed on the motor attachment face 41. A horizontal face is formed ata front portion of the center section 5, a pump attachment face 40 isformed on the horizontal face, and a hydraulic pump 50 is disposed onthe pump attachment face 40. Therefore, the hydraulic pump 50 isdisposed between the hydraulic motor 51 and the axles 7L and 7R whenviewed in the longitudinal direction of the bodywork. The pump shaft 3is vertically supported at a center of the pump attachment face 40. Thepump shaft 3 extends between the hydraulic motor 51 and the axles 7L and7R, passes through an upper wall of the upper housing 1, and projectswherein the input pulley 43 is mounted thereon.

[0032] A cylinder block 16 is disposed for rotation and sliding on thepump attachment face 40. Pistons 12, 12, are fitted for reciprocation ina plurality of cylinder bores of the cylinder block 16 through biasingsprings. A thrust bearing 11 a of a movable swash plate 11 is in contactwith bead portions of the pistons 12, 12. An opening portion 11 b isformed at a center of the movable swash plate 11 such that the pumpshaft 3 can pass through the opening portion 11 b. The pump shaft 3 alsofunctions as an input shaft, is disposed on a center rotational axis ofthe cylinder block 16, and is locked to the cylinder block 16 such thatthe pump shaft 3 and the cylinder block 16 cannot rotate with respect toeach other, thereby forming the hydraulic pump 50 of an axial pistontype.

[0033] By inclining a piston contact face of the movable swash plate 11through an arbitrary angle from a horizontal position with respect tothe center rotational axis of the cylinder block 16, it is possible tochange a discharge amount or a discharge direction of oil from thehydraulic pump 50. A back face of the movable swash plate 11 is formedinto a projecting arc portion. A recessed arc portion corresponding to ashape of the projecting arc portion is formed on an inner face of anupper portion of the upper housing 1. The projecting arc portion ofmovable swash plate 11 is formed as a cradle-type movable swash platethat slides in close contact with the recessed arc portion of the upperhousing 1.

[0034] In order to incline the movable swash plate 11, as shown in FIGS.4 and 7, a control shaft 35 parallel with the axle 7 is rotatablysupported on a right wall of the upper housing 1 on an opposite side tothe drive train for transmitting power to the differential gear 23. Acontrol arm 38 is mounted to an end portion of the control shaft 35extending to an outside of the housing and a swinging arm 39 is mountedto a housing inner end portion of the control shaft 35. The swinging arm39 is formed of a first arm 39 a and a second arm 39 b extendingradially from the control shaft 35 and a contact plate 39 e formed intoa shape of a sector.

[0035] The contact plate 39 e extends to a vicinity of an end face ofthe horizontal portion of the center section 5 in the lower housing 2and forms a sector-shaped contact face around an axial center of thecontrol shaft 35 such that the contact plate 39 e can be in contact withpiston bodies 64, 64 which will be described below in an entire rangecovered when the control lever 38 is rotated from a neutral position toa forward-side maximum position and a rearward-side maximum position asshown in FIG. 7. The contact plate 39 e may be formed as a separatemember independent of the control arm 39 if the contact plate 39 erotates with the control arm 39.

[0036] A projection 39 c is formed at a tip end portion of the secondarm 39 b. Because the axial center of the control shaft 35 is alignedwith a center of inclining of the movable swash plate 11, it is possibleto directly engage the projection 39 c with a groove portion formed inaside face of the movable swash plate 11. The control arm 39 isconnected to a speed change operating tool (not shown) such as a leverand a pedal provided to the vehicle through a linkage (not shown).

[0037] With the above structure, when the control arm 38 is rotatedalong the longitudinal direction of the bodywork, the swinging arm 39rotates in the longitudinal direction of the bodywork about the controlshaft 35 to incline the movable swash plate 11, thereby changing outputof the hydraulic pump 50.

[0038] An engaging pin 39 d is formed to project from a tip end of thefirst arm 39 a (FIG. 4). A neutral position recovering spring 31 of ahelical torsion spring type is fitted to an outside of the control shaft35 in the housing. Opposite ends of the neutral position recoveringspring 31 cross and extend toward the first arm 39 a. The opposite endportions of the neutral position recovering spring 31 pinch an eccentricshaft 33 mounted to an inner wall of the upper housing 1 in the vicinityof the control shaft 35 and the engaging pin 39 d between the oppositeend portions.

[0039] Therefore, when the control arm 38 is rotated to rotate theswinging arm 39 in order to change speed, one end side of the neutralposition recovering spring 31 is moved away from the other end side ofthe neutral position recovering spring 31 by the engaging pin 39 d whilethe other end side is stopped by the eccentric shaft 33, therebyapplying biasing force for recovering the neutral position to thecontrol lever 38. If operating force applied to the control arm 38 iscancelled, the engaging pin 39 d is retained in a neutral positiondetermined by the eccentric shaft 33 by the recovering force generatedon the one end side of the neutral position recovering spring 31. Aportion of the eccentric shaft 33 extending to the outside of thehousing is formed into an adjusting screw. By arbitrarily rotating anddisplacing the eccentric shaft 33 through the screw portion, theswinging arm 39 is displaced about the control shaft 35 through theneutral position recovering spring 31 and it is possible to adjust themovable swash plate 11 such that the movable swash plate 11 ispositioned in the accurate neutral position.

[0040] Pressure oil discharged from the hydraulic pump 50 is sent to thehydraulic motor 51 through an oil path in the center section 5. Astructure of the hydraulic motor 51 is shown in FIGS. 4 and 8. Acylinder block 17 is disposed for rotation and sliding on the motorattachment face 41 formed on the vertical face of the center section 5.A plurality of pistons 13, 13, are fitted for reciprocating in aplurality of cylinder bores of the cylinder block 17 through biasingsprings. Head portions of the pistons 13, 13 are in contact with a fixedswash plate 37. The fixed swash plate 37 is sandwiched and fixed betweenthe upper housing 1 and the lower housing 2.

[0041] A pair of arcuate ports (not shown) open at the pump attachmentface 40 of the horizontal portion of the center section 5 such thatsupplied or discharged oil from the cylinder block 16 can be introducedthrough the ports. As shown in FIG. 5, a pair of arcuate ports 41 a and41 b also open on the motor attachment face 41 of the vertical portionsuch that supplied or discharged oil from the cylinder block 17 can beintroduced through the ports.

[0042] In a thick-walled portion of the center section 5, a straightfirst oil path 5 a and a straight second oil path 5 b are formed inparallel with each other in upper and lower positions for respectivelyconnecting the arcuate ports on the pump attachment face 40 and thearcuate ports 41 a and 41 b on the motor attachment face 41. One of thearcuate ports on the pump attachment face 40 communicates with the oilpath 5 d formed in a diagonal direction shown in FIG. 7 and the oil path5 d communicates with the second oil path 5 b. These oil pathsconstitute a closed circuit for circulating the hydraulic oil betweenthe hydraulic pump 50 and the hydraulic motor 51. As shown in FIGS. 5and 7, check valves 54 and 55 are disposed at front end portions of thefirst oil path 5 a and second oil path 5 b in their extending direction.Also, an oil hole 5 c that communicates with both the check valves 54and 55 and opens downward at a lower face of the center section isprovided to a primary side (front portion) of the check valves 54 and 55such that the check valves 54 and 55 automatically open only insupplying the hydraulic oil.

[0043] As shown in FIG. 7, piston bodies 64, 64 constituting means forlessening a shock in recovering of the neutral position are arranged ina vertical direction at oil path ends formed perpendicularly to thefirst oil path 5 a and second oil path 5 b. Each piston body 64 has acylindrical shape and is formed at an axial center portion with anorifice 64 b to open the oil paths 5 a and 5 b to an outside of theclosed circuit through the orifice 64 b. In other words, when thecontrol arm 39 is in the neutral position, straight and vertical grooveportions 39 f each having a width slightly larger than a diameter ofeach of ends of the orifices 64 b, 64 b are formed on the contact plate39 e that faces the orifices 64 b, 64 b of the piston bodies 64, 64 andopen at the lower face of the contact plate 39 e.

[0044] By the groove 39 f, the closed circuit is allowed to communicatewith an oil reservoir within the housing through the orifices 64 b, 64b. By rotating the control arm 39 such that the movable swash plate isinclined through an angle greater than a predetermined angle from theneutral position, the orifices 64 b, 64 b and the groove portions 39 f,39 f are separated from each other. A surface of the contact plate 39 eexcluding the groove portions 39 f, 39 f and facing the orifices 64 b,64 b is formed to be smooth and a friction plate 68 is disposed at aportion facing the orifices 64 b, 64 b through the contact plate 39 eand is sandwiched and fixed between the upper housing 1 and the lowerhousing 2. As described below, if the piston bodies 64,64 advance whilereceiving hydraulic pressure, the contact plate 39 e is sandwichedbetween the piston bodies 64, 64 and the friction plate 68, therebyapplying rotational resistance to the contact plate 39 e.

[0045] In such a structure, if the speed change operating tool of thevehicle is operated to rotate the control lever 38 of the axle drivingsystem, the control arm 39 is rotated through the control shaft 35, theengaging projection 39 c is engaged with the engaging groove of themovable swash plate 11 to incline the movable swash plate 11, thedischarge amount of the hydraulic oil of the hydraulic pump is changed,and a rotation number of the motor shaft 4 of the hydraulic motor ischanged according to a rotation direction and a rotation amount of thespeed change operating tool to transmit power to the axle 7.

[0046] At this time, pressure proportional to load of the axle 7 isapplied to the higher-pressured oil, i.e., the first oil path 5 a or thesecond oil path 5 b and one of the piston bodies 64 is slid outward bythis pressure to push the contact plate 39 e of the control arm 39.Friction force generated by the pushing force is set at a smaller valuethan the spring force of the neutral position recovering spring 31. Anoperator operates the speed change operating tool with operating forcethat exceeds the friction force and the spring force. Because theorifice 64 b of the piston body 64 is closed by the smooth face of thecontact plate 39 e after inclining the movable swash plate through thepredetermined angle, the hydraulic oil circulating through the closedcircuit does not leak from the orifice 64 b and the volumetricefficiency of the HST is maintained satisfactorily.

[0047] In such a state, if the operator releases the operating forceapplied to the speed change operating tool, the control arm 39 is biasedby the spring force of the neutral position recovering spring 31 suchthat the control arm 39 rotates toward the neutral position. However, asdescribed above, because the friction force is generated between thepiston body 64 and the contact plate 39 e of the control arm 39,resistance is applied to the rotation toward the neutral position andthe control arm 39 gradually rotates toward the neutral position. Thus,sudden dynamic braking is not applied and a quick stop is not generated.When the control arm 39 rotates to the vicinity of the neutral position,the orifice 64 of the piston body 64 communicates with the grooveportion 39 f of the control arm 39, pushing pressure applied to thecontact plate 39 e and residual pressure in the closed circuit areallowed to escape, a shock of stop is lessened, and a neutral range ofthe HST is widened.

[0048] A bypass operating lever 60 for causing the first oil path 5 aand second oil path 5 b open into the oil reservoir is disposed at anupper portion of the upper housing 1 such that the axle can befreewheeling in tow. In other words, as shown in FIGS. 5 and 8, a baseportion of the bypass operating lever 60 is fixed to an upper end of abypass shaft 61 axially supported for rotation in a vertical directionby an upper wall of the upper housing 1 and a lower end of the bypassshaft 61 extends along one side face of a vertical portion of the centersection 5. A pushing pin 62 that can come in contact with a rotatingsliding face of the cylinder block 17 supported on the other side faceof the vertical portion is slidably supported in the vertical portion.An end face of the pushing pin 62 is brought into contact with a flatface 61 a formed on a side face of the lower end of the bypass levershaft 61.

[0049] Therefore, if the operator operates the bypass operating lever 60on the outside of the housing in tow of the vehicle, the bypass levershaft 61 is rotated, the flat face 61 a at the lower end of the bypasslever shaft 61 inclines to push the pushing pin 62 toward the cylinderblock 17, the pushing pin 62 separates the motor attachment face 41 andthe cylinder block 17 which have been in close contact with each other,and the first oil path 5 a and second oil path 5 b open into the oilreservoir of the housing through the arcuate ports 41 a and 41 b,thereby allowing the motor shaft 4 to rotate freely.

[0050] An annular oil filter 56 is disposed between a lower face of thecenter section 5 and an inner bottom face of the lower housing 2 suchthat a periphery of an opening portion at a lower end of the oil hole 5c is covered with the oil filter 56. The oil filter 56 is formed bysandwiching a ring-shaped porous member that is a filter main bodybetween upper and lower cover plates 57 and 58 and disposing acylindrical support cylinder 59 such as net or punching metal at aninner peripheral face portion of the porous member as shown in FIGS. 5and 7. Because an opening 57 a is formed at a center portion of theupper cover plate 57, filtered oil that has flowed from an outerperipheral portion of the oil filter 56 into an inside of the oil filter56 can flow into the oil hole 5 c of the center section 5 through theopening 57 a.

[0051] The cover plates 57 and 58 are formed of a steel sheet such as aniron sheet and a nickel sheet which can be magnetized and a magnet 63 isplaced on an upper face of an inner face of the lower cover plate 58 tomagnetize the lower cover plate 58. In this manner, iron powder includedin the reservoir of the first room R1 is collected by the lower coverplate 58 and even extremely fine iron powder that has passed through theoil filter 56 is collected by the magnet 63 or the lower cover plate 58and is not introduced into the closed circuit, thereby preventingdamaging of the sliding face and the like.

[0052] A position where the magnet 63 is disposed is not limited to theupper face of the lower cover plate 58 and the magnet 63 may be alsodisposed on a lower face of the lower cover plate 58 or at the uppercover plate 57. If the magnet 63 is disposed at the upper cover plate57, it is necessary to provide a bridge, a mount, or the like such thatthe magnet 63 can be hung within the oil filter 56.

[0053] If the magnet 63 is provided to the lower face of the lower coverplate 58, as shown in FIG. 9, a depression or a recessed portion 2 a isformed at the lower housing 2 at a lower portion where the oil filter 56is positioned to form a space where dust and the like accumulate. Threeor more projections 2 b, 2 b, are formed on an inner face of the lowerhousing 2 in peripheral positions of the space where the oil filter 56is positioned and the lower face of the lower cover plate 58 is placedon the projections 2 b, 2 b, thereby supporting the oil filter 56.

[0054] Thus, a passage is formed by the projections 2 b, 2 b, betweenthe lower cover plate 58 and the bottom face of the lower housing 2 andbetween the projections 2 b, 2 b, dust and the like pass through thepassage and accumulate in the recessed portion 2 a that is less subjectto flow of oil when the oil is stirred, and the iron powder is collectedby the magnet 63. By the projections 2 a,2 a, the lower cover plate 58is disposed in a higher position, thereby forming a space where themagnet 63 is disposed.

[0055] Furthermore, if there is extremely fine iron powder that haspassed through the oil filter 56, the iron powder is collected by anupper face of the lower cover plate 58 because the lower cover plate 58is magnetized by the magnet 63.

[0056] The motor shaft 4 is locked onto a rotation axial center of thecylinder block 17 such that the motor shaft 4 cannot rotate with respectto the cylinder block 17. The hydraulic motor shaft 4 is oriented in asubstantially horizontal direction. One end of the motor shaft 4 issupported in a bearing hole in the motor attachment face 41 of thecenter section 5, the other side of the motor shaft 4 is supportedthrough a bearing 76 on the inner wall 8 formed at the joint facebetween the upper housing 1 and the lower housing 2, and a tip endprojects into the second room R2. A bearing with a seat is used as thebearing 76 so as to separate the first room R1 and the second room R2.

[0057] The drive train for transmitting power from the motor shaft 4 tothe differential gear system 23 is formed of a gear 25 secured onto themotor shaft 4 projecting into the second room R2, a large-diameter gear24 that constantly meshes with the gear 25 and is supported on thecounter shaft 26, a small-diameter gear 21 supported on the countershaft 26 rotating with the large diameter gear 24, and a ring gear 22 ofthe differential gear 23 with which the small-diameter gear 21constantly meshes as shown in FIGS. 4 and 6. The counter shaft 26 isdisposed within the second room R2 to be adjacent to and orthogonal tothe pump shaft 3.

[0058] One end of the counter shaft 26 is supported on a side wall ofthe housing, i.e., at the joint face between the upper housing 1 and thelower housing 2 and the other end of the counter shaft 26 is supportedon the inner wall 8 of the housing, i.e., at the joint face between theupper housing 1 and the lower housing 2. Speed of rotation output fromthe motor shaft 4 is reduced by the large-diameter gear 24, the smalldiameter gear 21, and the ring gear 22 to drive the axles 7L and 7Rthrough the differential gear 23.

[0059] A brake disc 19 formed integrally with the gear 25 is securedonto a tip end portion of the motor shaft 4 positioned within the secondroom R2. As shown in FIG. 4, a brake pad 29 is disposed between a rearside of an upper portion of the brake disc 19 and an inner face of theupper housing 1 and a pressing body 72 and a brake operating shaft 14are disposed successively with respect to the brake disc 19 in a portionsurrounded by the brake disc 19 and the inner wall 8 of the housing on aside (right side of the brake disc 19) of the brake disc 19 opposite tothe brake pad 29.

[0060] The brake operating shaft 14 is disposed in a vertical directionand supported rotatably by the upper housing 1 and the lower housing 2.An upper end of the brake operating shaft 14 projects upward from thehousing and a brake arm 27 (FIG. 3) is fixed to the upper end. A flatnotch 14 a is formed on an outer face of a midway portion of the brakeoperating shaft 14 within the housing such that the operating shaft 14has a D shape in a plan sectional view, the pressing body 72 is broughtinto contact with the notch 14 a, movement of the pressing body 72 inrightward and leftward directions is limited by the notch 14 a, andfront and rear opposite sides of the pressing body 72 are guided by theinner face of the upper housing I such that the pressing body 72 canslide only in leftward and rightward directions. Therefore, if the brakearm 27 is rotated, the brake operating shaft 14 is rotated, an endportion of the notch 14 a pushes a back face of the pressing body 72,and the brake disc 19 is sandwiched between the brake pad 29 and thepressing body 72 to brake the motor shaft 4.

[0061] The first room R1 and the second room R2 are filled with commonlubricating oil to form the oil reservoir. As shown in FIGS. 4 to 8, acommunicating room 9 is formed at an upper portion of the inner wall 8that partitions the inside of the housing into the first room R1 and thesecond room R2. An oil inlet 9 a communicating with the first room R1and an oil inlet 9 b communicating with the second room R2 open into aside face and a bottom of the communicating room 9. An opening portion 1c, to which a filter member that will be described below is mounted, isformed at the upper housing above the oil inlets, and the openingportion 1 c is closed by a lid 65.

[0062] A mounting seat 66 formed by press forming an iron sheet into acup shape is placed on a bottom face of the communicating room 9 and amagnet 71 as a filter member for removing impurities is placed and fixedonto the mounting seat 66. The magnet 71 is formed into a disc shape,and as shown in FIG. 10, an elongated hole 66 a is formed on an upperface of the mounting seat 66. By inserting the magnet 71 into theelongated hole 66 a and bringing tongue chips 66 b extending fromopposite sides of the elongated hole 66 a to face each other intoresilient contact with opposite faces of the magnet 71, the magnet 71and the mounting seat 66 are integrated with each other. The integratedmagnet 71 and mounting seat 66 are inserted into the communicating room9 that opens at an upper wall of the upper housing 1 and the opening isclosed by the lid 65, thereby achieving completion.

[0063] A reference numeral 66 c in FIG. 10 designates notches, eachformed by partially notching a lower end face of the mounting seat 66. Awidth of the notch 66 c is equal to a thickness of a portion of theinner wall 8 positioned at the bottom face of the communicating room 9.By inserting the portions of the inner wall 8 into the notches 66 c whenthe mounting seat 66 is placed on the bottom face of the communicatingroom 9, rotation of the magnet 71 within the communicating room can beprevented.

[0064] The magnet 71 is fixed such that the magnet 71 is oriented to bediagonal with respect to the oil inlets 9 a and 9 b so as to increase acontact area in flowing of the oil. However, the magnet 71 may have arectangular shape and a shape of the magnet 71 is not limited.

[0065] With the above structure, iron powder generated in the first roomR1 and the second room R2 when the oil within the housing circulatesbetween the first room R1 and the second room R2 is attracted by themagnet 71 and adheres to the magnet 71 and the mounting seat 66 tomaintain the oil that has accumulated in the first room R1 in a cleanstate, thereby improving durability of the HST.

[0066] As shown in FIGS. 2 and 6, an oil circulating hole 1 a opens atthe upper wall face of the upper housing 1 forming the second room R2 ina position where the hole does not interfere with the input pulley 43and the cooling fan 44. A joint pipe portion 1 b is formed on aperiphery of the oil circulating hole 1 a. A tubular reservoir tank 10formed of a rubber hose or a resilient member is fitted with the jointpipe portion 1 b such that the reservoir tank 10 communicates with thesecond room R2 in a fluidic manner. A lower portion of the reservoirtank 10 is fastened and fixed by the joint pipe portion 1 b and bands 69a. An opening at an upper end of the reservoir tank 10 is closed by abreather cap 70 and fastened and fixed by bands 69 b.

[0067] If the first and second rooms R1 and R2 are filled with oil afterassembling the axle driving system, an oil level OL is determined withinboth the rooms R1 and R2 as shown in FIGS. 5 to 8. The oil level OL isuniform because both the rooms R1 and R2 communicate with each otherthrough the communicating room 9. If a volume of the oil within thefirst room R1 varies depending on whether the HST is driven, the oillevel OL shifts upward or downward from the position shown in thedrawings. An air layer with a variable volume is formed above the oillevel OL within the reservoir tank 10 that opens into the atmospherethrough the breather cap 70. The air layer allows variation in thevolume of the oil.

[0068] Thus, the hydraulic oil expands and the volume of the hydraulicoil increases when a temperature of the hydraulic oil within the oilreservoir increases due to driving of the HST. The volume can beadjusted by causing the increase in the volume to flow into thereservoir tank 10 and a vertical length of the tube portion of thereservoir tank 10 is set at such a value as to keep at least a volumecorresponding to an oil amount by which the volume of the housingincreases.

[0069] The reservoir tank 10 can be easily mounted by only inserting thereservoir tank 10 in to the joint pipe portion 1 b on the outer wall ofthe housing and fastening the reservoir tank 10 by the band 69 a. Asshown in FIG. 2, if the chute 106 and the like exist above the housing,the reservoir tank 10 can be bent naturally to make way for the chute106 and the like because of resiliency of the reservoir tank 10 itself.

[0070] Therefore, it is possible to reduce limitations on disposition ofthe reservoir tank 10.

[0071] As described above, the axle driving system according to theinvention is a system suitable for driving an axle of a field-workvehicle, a vehicle of construction equipment, a mowing vehicle, a snowremoval vehicle, or the like and especially suitable to a lawn tractorof a rear discharge method having a chute above the housing.

What is claimed is:
 1. An axle driving system wherein a tubularreservoir tank is mounted to stand on an upper face of an upper wallface of a housing that houses a hydrostatic transmission (hereafterreferred to as HST) including a hydraulic pump and a hydraulic motor andsaid reservoir tank communicates with an oil reservoir within saidhousing.
 2. An axle driving system according to claim 1, wherein saidhousing is partitioned into a first room, housing said HST and a secondroom, housing an axle and a gear train for transmitting power from saidhydraulic motor to said axle, both said rooms communicate with eachother such that oil with which both said rooms are filled can circulatebetween both said rooms, and said reservoir tank is disposed on saidsecond room.
 3. An axle driving system according to claim 2, wherein afilter member for removing impurities included in oil passing through acommunicating position connecting said first room and said second roomis disposed in said communicating position.
 4. An axle driving systemaccording to claim 3, wherein said filter member is formed of a magnet.5. An axle driving system wherein a closed circuit is formed byproviding an oil path to a center section to which a hydraulic pump anda hydraulic motor in an HST are mounted, an oil hole opening at saidcenter section for supplying hydraulic oil to said closed circuit isconnected to an oil filter disposed in an oil reservoir, and a magnet isdisposed in said oil reservoir in a vicinity of said oil filter.
 6. Anaxle driving system according to claim 5, wherein said magnet isdisposed such that said magnet acts on said hydraulic oil after passingthrough said oil filter and before entering said oil hole.
 7. A mowertractor comprising: a chute for mowed lawn; a transmission belt disposedon one lateral side of said chute; and a reservoir disposed on the otherlateral side of said chute opposite to said transmission belt.
 8. Amower tractor comprising: an axle driving apparatus; a housing for saidaxle driving apparatus; a chute for mowed lawn; and a reservoir disposedsidewise from said chute so as to avoid abutting against said chute. 9.A mower tractor comprising: an engine having an engine output pulley; anaxle driving apparatus having an input pulley disposed in one of frontand rear of said engine output pulley; an idler pulley for said axledriving apparatus disposed in the other of front and rear of said engineoutput pulley; a belt looped over said engine output pulley, said inputpulley and said idler pulley, wherein said belt is disposed on onelateral side of said input pulley; and a reservoir disposed on the otherlateral side of said input pulley opposite to said belt.